var str = "3931";
var begin = '<img src="images/dg';
var middle = ".gif\" width=\"16\" height=\"21\" alt=\"";
var last = "\">";
document.write('<div>');
for(x = 0;x < str.length; x++)    {
    str1 = str.charAt(x);
    document.write(begin + str1 + middle + str1 + last);
}
document.write('</div>');